Sintered sliding member having exceptional corrosion resistance, heat resistance, and wear resistance; and method for producing said member

ABSTRACT

A sintered sliding material with excellent corrosion resistance, heat resistance, and wear resistance is provided. The sintered sliding material has a composition made of: 36-86 mass % of Ni; 1-11 mass % of Sn; 0.05-1.0 mass % of P; 1-9 mass % of C; and the Cu balance including inevitable impurities. The sintered sliding material is made of a sintered material of a plurality of grains of alloy of Ni—Cu alloy or Cu—Ni alloy, the Ni—Cu alloy and the Cu—Ni alloy containing Sn, P, C, and Si; has a structure in which pores are dispersedly formed in grain boundaries of the plurality of the grains of alloy; and as inevitable impurities in a matrix constituted from the grains of alloy, a C content is 0.6 mass % or less and a Si content is 0.15 mass % or less.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.15/510,561, filed Mar. 10, 2017, which is a U.S. National PhaseApplication under 35 U.S.C. § 371 of International Patent ApplicationNo. PCT/JP2015/075751, filed Sep. 10, 2015, and claims the benefit ofJapanese Patent Application No. 2014-185453, filed on Sep. 11, 2014, allof which are incorporated herein by reference in their entirety. TheInternational Application was published in Japanese on Mar. 17, 2016 asInternational Publication No. WO/2016/039423 under PCT Article 21(2).

FIELD OF THE INVENTION

The present invention relates to a sintered sliding material withcorrosion resistance, heat resistance, and wear resistance and a methodfor producing the same used: under a corrosive environment, which is ina liquid of sea water or the like or includes the snow melting agent; ina corrosive atmosphere, which is at a high temperature and containsexhaust gas; and in a fuel, which contains sulfur, organic acid, or thelike.

BACKGROUND OF THE INVENTION

An example of the sliding part, which is used in the corrosiveenvironment in liquid, is a sliding material forming a bearing thatsupports the rotating shaft in the casing of the motor fuel pumpprovided to the engine utilizing liquid fuel such as gasoline and lightoil. In addition, as examples of the sliding material used in thecorrosive atmosphere such as sea water and the snow melting agent, thesliding material for the outboard motor; and the exhaust throttle valveused for the diesel exhaust gas purification system, are known.

In addition, as examples of the sliding material used in the corrosiveatmosphere of high temperature, exhaust gas, or the like, the exhaustthrottle valve used for the diesel exhaust gas purification system; andthe recirculation exhaust gas flow control valve of the EGR (Exhaust GasRecirculation) type internal combustion engine, are known.

The engine that uses the liquid fuel such as gasoline and light oil withthe motor fuel pump is used all over the world; and high wear resistanceis demanded for the motor fuel pump. Qualities of liquid fuel varyworldwide depending on locations. Thus, depending on the locations,there is an area, in which bad quality gasoline with poor quality isused. Thus, corrosion resistance against the bad quality gasoline isneeded for the sliding material of the bearing used for the motor fuelpump.

Conventionally, as an example of the bearing sliding material of thistype of usage, the sliding material made of the sintered Cu—Ni-basedalloy, which has the composition of Cu-21 to 35% Ni-5 to 12% Sn-3 to 7%C-0.1 to 0.8% P, is known (refer Japanese Patent No. 4521871 (B)).

In addition, as a sliding material used: in the high temperaturecorrosive atmosphere; and under the corrosive environment due to saltsuch as sea water and the snow melting agent, the sliding materials madeof stainless or sintered alloy, which is subjected to a surfacetreatment such as nitriding, is known (refer Japanese Patent No. 5386585(B)).

In addition, as a sintered sliding part having excellent corrosionresistance and wear resistance under the high temperature environment,the sintered sliding part, in which the amounts of Cu and Si are definedand boron nitride is added in a predetermined ratio, is known (referJapanese Patent No. 5337884 (B)).

Technical Problem

The bearing of the motor fuel pump described in Japanese Patent No.4521871 (B) is made of the sintered Cu—Ni-based alloy having thecomposition of: 21-35 mass % of Ni; 5-12 mass % of Sn; 3-7 mass % of C;0.1-0.8 mass % of P; and the Cu balance including inevitable impurities.In this sintered alloy, pores are dispersed in the matrix in theporosity of 8-18%; P is contained most in the grain boundary part; andthe sintered alloy has the structure in which free graphite isdistributed in the above-mentioned pores. The sintered alloy has thestructure, in which the alloy layer with high Sn concentrationcontaining Sn at 50 mass % or more, on the inner surface of the openpores formed to be opened on the surface of the bearing made of thissintered Cu—Ni-based alloy, on at least periphery of the opening of thepores, and on the inner surface of the internal pores internallyexisting in the inside of the bearing.

The sintered sliding material described in Japanese Patent No. 5386585(B) contains: 63-90 mass % of Ni; at least one of 2-20 mass % of Sn and0.1-1.2 mass % of P; and the Cu balance including inevitable impurities.

The sintered sliding material described in Japanese Patent No. 5337884(B) has the composition containing: 7.7-30.3 mass % of Cu; 2.0-20.0 mass% of Sn; 0.3-7.0 mass % of boron nitride; and the Ni balance includinginevitable impurities.

The sintered sliding material used for the motor fuel pump is immersedin liquid fuel at all times. As liquid fuel, not only the conventionalliquid fuel such as the gasoline and light oil but alsoalcohol-containing gasoline utilizing energy from biomass is put topractical use depending on the area speaking on a global scale, becauseof resource depletion and attempt to reduce CO₂ emission. Recently,gasoline with high alcohol addition rate tends to be used.

However, the alcohol-containing gasoline lacks oxidative stability underhigh-temperature high-humidity environment or the like; and it ispossible that the alcohol-containing gasoline is converted to include alarge amount of corrosive liquid such as carboxylic acid. Therefore,excellent corrosion resistance beyond conventional is required for thesintered sliding material used for the motor fuel pump.

In this context, the corrosion resistance of the Cu—Ni—Sn—P—C-basedsintered sliding material disclosed in Japanese Patent No. 4521871 (B)against even more highly-concentrated acid is not sufficient. In thecommon corrosion resistant material, it is known that having a uniformstructure is beneficial for improving corrosion resistance. In addition,increasing the sintering temperature is effective for forming theuniform structure in the sintered material.

However, in the sintered sliding material disclosed in Japanese PatentNo. 4521871 (B), dimensional change is increased if the sinteringtemperature of 890-970° C. is increased further; and there is atechnical problem that production yield is deteriorated. For example, inthe sintered sliding material described in Japanese Patent No. 4521871(B), the alloy layer with high Sn concentration is formed in the grainboundaries of the Cu—Ni alloy grains. Thus, the dimensional change isincreased if the sintering temperature is increased for obtaining theuniform structure. In this case, there are problems of: not being ableto shape the sintered material by placing it in a mold; and not beingable to obtain the intended dimensional accuracy, during sizing forsetting the dimension as the final product.

Under the circumstance described above, the inventors of the presentinvention conducted extensive studies about this type of sinteredmaterial. They focused on influence of extremely trace amount ofimpurities, such as C, Si, and the like, which is included in the matrixof the sintered sliding material, on a Cu—Ni—Sn—P—C-based sinteredsliding material with a metal structure, in which the alloy layer withhigh Sn concentration having been precipitated in grain boundaries inthe past is reduced by increasing the sintering temperature. Then, theyfound that these impurity elements greatly affect the sinteringdimensional change even if they are in extremely trance amounts, andmade the present invention.

The present invention is made under circumstances described above. Thepurpose of the present invention is to provide a sintered slidingmaterial having excellent corrosion resistance, heat resistance, andwear resistance by controlling the amounts of C and Si as impuritiesincluded in the matrix of the sintered material.

SUMMARY OF THE INVENTION Solution to Problem

An aspect of the present invention is a sintered sliding material withexcellent corrosion resistance, heat resistance, and wear resistance(hereinafter, referred as “the sintered sliding material of the presentinvention”) having a composition made of: 36-86 mass % of Ni; 1-11 mass% of Sn; 0.05-1.0 mass % of P; 1-9 mass % of C; and the Cu balanceincluding inevitable impurities, wherein the sintered sliding materialis made of a sintered material of a plurality of grains of alloy ofNi—Cu alloy or Cu—Ni alloy, the Ni—Cu alloy and the Cu—Ni alloycontaining Sn, P, C, and Si, the sintered material has a structure inwhich pores are dispersedly formed in grain boundaries of the pluralityof the grains of alloy, and as inevitable impurities in a matrix (basematerial) constituting the grains of alloy, a C content is 0.6 mass % orless and a Si content is 0.15 mass % or less.

In the sintered sliding material of the present invention, a porosity ofthe sintered material may be 8-28%.

In the sintered sliding material of the present invention, free graphitemay interpose in the grain boundaries of the sintered material.

Other aspect of the present invention is a method of producing asintered sliding material with excellent corrosion resistance, heatresistance, and wear resistance (hereinafter referred as “the method ofproducing a sintered sliding material of the present invention”), themethod including the steps of: obtaining a mixed powder by using atleast one of a Cu—Ni alloy powder and a Ni—Cu alloy powder, in which a Ccontent is 0.6 mass % or less and a Si content is 0.15 mass % or less asinevitable impurities, in obtaining the mixed powder by mixing aplurality of powders containing one or more among Cu, Ni, Sn, P, and Cin such a way that a total composition of the mixed powder becomes:36-86 mass % of Ni; 1-11 mass % of Sn; 0.05-1.0 mass % of P; 1-9 mass %of C; and the Cu balance; producing a green compact by pressing themixed powder; and

obtaining a sintered sliding material having a structure containing: anintegrated matrix; and free graphite dispersed in a plurality of poresby sintering the green compact at 960-1140° C. for a plurality of grainsof alloy made of a Cu—Ni alloy or a Ni—Cu alloy to disperse theplurality of pores in grain boundaries of the plurality of grains ofalloy.

In the method of producing a sintered sliding material of the presentinvention, the mixed powder may be obtained by mixing: at least one of aCu—Ni alloy powder and a Ni—Cu alloy powder; a Sn powder; a Cu—P alloypowder; and C powder.

In the method of producing a sintered sliding material of the presentinvention, as inevitable impurities in the matrix, a C content may be0.6 mass % or less, a Si content may be 0.15 mass % or less.

In the method of producing a sintered sliding material of the presentinvention, a porosity of the sintered material may be 8-28%.

Advantageous Effects of Invention

According to the present invention, a sintered sliding material, whichhas excellent wear resistance and lubricity; and excellent corrosionresistance under high-temperature environment as a sliding material usedunder high-temperature corrosive environment, can be provided, sincegrains of Ni—Cu alloy or Cu—Ni alloy are sintered; and it is obtained asthe sintered sliding material in which free graphite disperses the poresin grain boundaries.

In addition, by setting the C content and the Si content as impuritiesincluded in grains of the Ni—Cu alloy or the Cu—Ni alloy to the definedamounts or less, a sintered sliding material, which does not easilycause large dimensional change and can be produced with good yield, canbe provided.

In addition, a sintered sliding material, which: is suitable for thebearing part or the like used immersed in gasoline at all times such asthe motor fuel pump; has excellent corrosion resistance underhigh-temperature environment even in the case where it is immersed inmixed gasoline including light oil, alcohol, etc., and corrosive liquidsuch as organic acid depending on the area, can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an example of a ring-shaped bearingpart formed of the sintered sliding material according to the presentinvention.

FIG. 2 is an enlarged structural diagram of a sintered sliding materialconstituting the bearing part.

FIG. 3 is an exploded side view showing an example of a fuel pumpincluding the bearing part.

FIG. 4 is a structural photographs showing the corrosion resistance testresults of organic acid-containing gasoline on the surface of eachsample obtained in Example and Comparative Example in comparison.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention is explained in reference todrawings below.

In the drawings used for the explanations below, a characteristic partis shown as an enlarged manner occasionally for emphasizing thecharacteristic part for convenience; and the dimension ratio of eachconstituent or the like is not necessarily the same as the actual case.In addition, a part not corresponding to the characteristic part isomitted in the drawings occasionally for the same purpose.

FIG. 1 shows the ring-shaped bearing part 1 made of the sintered slidingmaterial according to the present invention. The bearing part 1 isconstituted from the sintered sliding material having the sectionalstructure shown in FIG. 2, for example. The bearing part 1 is used asthe bearing part of the motor fuel pump 2 shown in FIG. 3, for example.

In the motor fuel pump 2 shown in FIG. 3, the motor (armature) 5 isprovided surrounded by the magnet 4 in the cylindrical casing 3. Bothends of the rotating shaft 6 of the motor 5 are rotatably supported bythe bearing parts 1, each of which is provided in the casing 3. In thestructure shown in FIG. 3, the impeller 7 is attached to one end side ofthe rotating shaft 6; and the narrow gasoline passage is formed along:the outer periphery of the impeller 7; the outer periphery of the motor5; and the gap between the bearing parts 1, 1 and the rotating shaft 6.

In the motor fuel pump 2, the impeller 7 is rotated by the rotation ofmotor 5; gasoline is imported in the casing 3 from the inlet 8 providedto the one end side of the casing 3 by the torque of the impeller 7; andthe gasoline flows along the above-described gasoline passage. Then, thegasoline is discharged from the outlet 9 provided to the other end sideof the casing 3.

The motor fuel pump 2 is provided to the inside of the fuel tank ofinternal-combustion engine in such a way that it is immersed ingasoline, for example. The outlet 9 of the fuel pump 2 is connected tothe fuel ejector through the filter device and the injector, which areomitted from depiction in the drawing.

The motor fuel pump 2 shown in FIG. 3 is used in the state where it isimmersed in gasoline at all times; and the bearing parts 1 supportingthe rotating shaft 6 are used in the state where they are immersed inthe gasoline at all times too. Thus, excellent corrosion resistanceagainst gasoline is needed for the bearing parts 1.

Thus, the bearing part 1 of the present embodiment is made of thesintered sliding material 15 having the structure in which the pores 12are dispersedly distributed in the grain boundary parts of multiplealloy grains 11 in the cross section as shown in the structural diagramin FIG. 2; and the free graphite 13 are dispersed in insides of thepores 12. The alloy grains 11 are made of the Cu—Ni alloy grains or theNi—Cu alloy grains including Sn, P, and C; and the matrix of thesintered sliding material 15 is constituted from the multiple alloygrains 11, the dispersedly distributed pores 12, and the free graphite.

The method of producing the sintered sliding material 15 will bedescribed in detail later. The sintered sliding material 15 can beobtained by: uniformly mixing predetermined amounts of one or both ofthe Cu—Ni alloy powder and the Ni—Cu alloy powder, the Sn powder, theCu—P powder, and the graphite powder; press molding the mixed powder;and sintering the obtained green compact at 960-1140° C., for example.

Excellent sliding characteristics and corrosion resistance are ensuredby the alloy grains 11 made of the Cu—Ni alloy grains or the Ni—Cu alloygrains, which constitutes the matrix. In addition, high lubricity can beobtained by lubrication action of the free graphite, which isdistributed in the pores 12 dispersedly distributed in the matrix of thebearing part 1 and has high lubricity. Moreover, wear resistance isimproved further by action of fluid lubrication film formed by theliquid fuel provided from the outer periphery of the bearing part 1 tothe inner periphery of the bearing part 1 through the pores 12 existingin the inside of the bearing part 1. In addition, alloying of the mainphase can be strengthened by reducing the precipitation of the grainboundary phase for the bearing part 1 to show high strength. As aresult, it is possible for the bearing part 1 to be thin-layered orreduced in the diameter.

It is preferable that the composition ratio of the sintered slidingmaterial 15 includes: 36-85 mass % of Ni; 1-11 mass % of Sn; 0.05-1.0mass % of P; and 1-9 mass % of C. In addition, it is preferable that asinevitable impurities included in the matrix constituted from the alloygrains 11, the C content is 0.6 mass % or less and the Si content is0.15 mass % or less.

Reasons for defining each of the composition ratio are explained below.

[Ni: 36-86%]

Addition of Ni is effective on giving excellent strength, wearresistance and corrosion resistance. If the Ni content were less than36%, corrosion resistance as the sintered sliding material would not besufficient. If the Ni content were 86% or more, sliding characteristicsof the sintered sliding material would be reduced.

By selecting a proper sintering condition for the structure of thesintered sliding material, the Ni content of which is 36-86%, to be auniform structure excluding solid lubricant, corrosion resistance isimproved. A testing piece, the Ni content of which is 89%, hardness andstrength of the testing piece itself are too high; and the shaft isdamaged. Thus, it is not preferable.

Although it is not necessarily indispensable configuration, a morepreferable Ni content is 40 mass % to 80 mass %. An even more preferableNi content is 45 mass % to 70 mass %.

[Sn: 1-11%]

Addition of Sn is effective on improving corrosion resistance, strength,and wear resistance. If the Sn content were less than 1%, corrosionresistance as the sintered sliding material is reduced; and sufficientstrength cannot be obtained. If the Sn content were 12% or more, itwould be possible that Sn precipitates on the surface of the sinteredmaterial. In addition, the dimension of the sintered sliding materialvaries; and dimensional consistency is destabilized during sintering.Thus, it is not preferable for Sn to be included at 12% or more insintered sliding material of the present embodiment.

Although it is not necessarily indispensable configuration, a morepreferable Sn content is 3 mass % to 11 mass %. An even more preferableSn content is 4 mass % to 10 mass %.

[P: 0.05-1.0%]

Addition of P is effective on improving sinterability and strength ofthe matrix in the sintered sliding material of the present embodiment.However, if the P content were less 0.05%, the effect of improvingsinterability would not be obtained sufficiently; and sufficientstrength would not be obtained. On the other hand, if P were added at1.25% or more in the sintered sliding material of the presentembodiment, the liquid phase of Cu—P would be enlarged during sintering.In this case, levels of deformation and dimensional change become toohigh, and not preferable.

Although it is not necessarily indispensable configuration, a morepreferable P content is 0.1 mass % to 0.8 mass %. An even morepreferable P content is 0.1 mass % to 0.6 mass %.

[C: 1-9%]

Mainly, C exists in the pores dispersedly distributed in the matrix ofthe sintered sliding material as free graphite. Addition of C iseffective on giving excellent lubricity to the sintered sliding materialand improving wear resistance. If the C content were less than 1%, thelubricity effect would not be obtained; and the sintered slidingmaterial would not be able to exhibit the function as the sinteredsliding material. If the C content were 9% or more, the dimension andweight of the sintered sliding material during molding would vary; andthe dimensional consistency of the sintered sliding material duringsintering would be destabilized. Thus, it is not preferable.

Although it is not necessarily indispensable configuration, a morepreferable C content is 2 mass % to 8 mass %. An even more preferable Ccontent is 3 mass % to 8 mass %.

[C Content and Si Content in the Cu—Ni Alloy Powder or the Ni—Cu AlloyPowder]

It is not preferable that the C content (carbon content) is 0.61% ormore; or the Si content is 0.15% or more, as the inevitable impuritiesin the Cu—Ni alloy powder or the Ni—Cu alloy powder, each of which isthe source material when the sintered sliding material is produced bysintering, since it causes to abnormal expansion; and the dimensionalconsistency of the sintered sliding material is destabilized. If the Ccontent as impurities in the powder were set to less than 10 ppm, theproduction cost of the raw material for removal of C from the rawmaterial powder would be extremely high. Thus, it is not preferable.

Because of this, it is preferable that the C content is 0.61 mass % orless and a Si content is 0.15 mass % or less as inevitable impurities inthe Cu—Ni alloy powder or the Ni—Cu alloy powder.

Although it is not necessarily indispensable configuration, a morepreferable range of the C content is 0.002 mass % to 0.61 mass % asinevitable impurities in the Cu—Ni alloy powder or the Ni—Cu alloypowder. Similarly, although it is not necessarily indispensableconfiguration, a more preferable range of the Si content is 0.015 mass %to 0.15 mass % as inevitable impurities in the Cu—Ni alloy powder or theNi—Cu alloy powder.

The sintered sliding material obtained by using these alloy powdersshows the same tendency in terms of the C and Si contents in impurities.If the C content in the sintered material were 0.6% or more or the Sicontent in the sintered material were 0.15% or more, the sinteredmaterial would be deformed; and dimensional consistency is destabilizedfor the yield to be deteriorated. Thus, it is not preferable.

[Porosity: 8-25%]

The alloy grains 11 constituting the matrix of the sintered slidingmaterial 15 is made of the Cu—Ni alloy grains or the Ni—Cu alloy grains.The pores dispersedly distributed in the matrix made of these alloygrains 11 have an action to relax strong impact and high pressure loadedon the bearing part 1 under the condition where the liquid fuel passesat high pressure and high speed as described above, thereby suppressingwear on the bearing part 1 significantly. However, if the porosity wereless than 8%, the action would not be exhibited sufficiently since theratio of the pores distributed in the matrix becomes too low. If theporosity exceeded 28%, strength as the bearing part would be reduced.Therefore, the upper limit of the porosity is set to 28%.

Although it is not necessarily indispensable configuration, a morepreferable range of the porosity is 10% to 20%. An even more preferablerange of the porosity is 12% to 18%.

[Method of Producing the Sintered Sliding Material]

In order to produce the sintered sliding material 15 of the presentembodiment, the Cu—Ni alloy powder or the Ni—Cu alloy powder; the Cupowder; the Ni powder; the Cu—P powder; the graphite powder; and the Snpowder, each of which has a predetermined average grain size in therange of about 10-100 μm, are prepared as starting materials.

After blending each of these powders to obtain the final goalcomposition ratio, 0.1-1.0% of lubricant such as zinc stearate and thelike, for example about 0.5%, is added to the mixture; and the mixtureis uniformly mixed for about tens of minutes by a mixer to obtain themixed powder. Next, the mixed powder is poured in the mold of a pressingmachine to perform press molding and to obtain a green compact in anintended shape, such as in a ring-shape, for example.

The intended ring-shaped sintered sliding material can be obtained bysintering the green compact at a predetermined temperature in the rangeof 960-1140° C. in the endothermic gas atmosphere, which is obtained bymixing natural gas and air and passing the mixed gas thorough heatedcatalyst to be decomposed and denatured, for example.

During sintering, Sn and Cu—P, which are low melting point raw materials(about 232° C., and about 718° C., respectively), are melted in thesintering process; and Sn and P diffuse into the grains made of theCu—Ni alloy powder or the Ni—Cu alloy powder to be alloyed. Because ofthis, the structure shown in FIG. 2, in which the free graphite 13exists in the pore parts in the grain boundaries of the Cu—Ni alloygrains or the Ni—Cu alloy grains in which Sn or P is solid melted, isobtained after sintering.

In the case where the Cu—Ni alloy powder or the Ni—Cu alloy powder isproduced, the atomizing method in which powdering is performed byquenching from the alloy melt is used. In this case, the amounts of Cand Si included in the above-mentioned alloy powders can be reduced byproperly choosing: the addition amounts of C and Si used fordesulfurization; the material of the crucible; and time in which thealloy is melted, by controlling the melting temperature of the alloy,and the like.

EXAMPLES

The present invention is explained in more detail by showing Examplesbelow. However, the present invention is not limited by the descriptionsof Examples.

Example 1

As raw materials, the Cu—Ni powder and the Ni—Cu powder; the Sn atomizedpowder with the grain size of 250-mesh; the Cu-8% P atomized powder withthe grain size of 200-mesh; and the graphite powder were prepared. Theatomized powders were obtained by the atomizing method, in which alloymelt having the intended composition was formed in a crucible in a highfrequency melting furnace; and the alloy melt was quenched by spoutingout the alloy melt from the ejection nozzle provided on the bottom partof the crucible into the inside of water body.

These raw material powders were blended to obtain the final componentcompositions shown in Table below. Then, 0.5% of zinc stearate wasadded, and the mixture was mixed for 20 minutes by a V-type mixer. Then,the mixture was subjected to press molding to produce a green compact.Next, the green compact was sintered at the predetermined temperature inthe range of 960-1140° C. in the endothermic gas atmosphere, which wasobtained by mixing natural gas and air and passing the mixed gasthorough heated catalyst to be decomposed and denatured to obtain thesintered sliding material.

Each of the produced sintered sliding materials had the dimension of: 10mm of the outer diameter; 5 mm of the inner diameter; and the 5 mm ofthe height. They were the ring-shaped sintered sliding materials (thebearing parts) made of the sintered Ni—Cu—Sn-based alloy having thecomponent compositions shown Table below. Samples Nos. 1-22 of Examplesof the present invention; and samples Nos. 23-34 of ComparativeExamples, all of which were identically-shaped ring-shaped test pieces,were produced and subjected to the tests described below.

In the raw material powders, the C and S contents, which were includedin the Cu—Ni powder and Ni—Cu powder as impurity elements, werecontrolled by adjusting the amount of impurities included in the rawmaterials before the atomizing treatment, in which the Cu—Ni powder andthe Ni—Cu powder were produced.

Specifically, samples Nos. 1-8 were produced by blending powders so asto obtain the compositions shown in Table 1 by using the raw materialshaving the impurity amounts (C contents and Si contents) shown inTable 1. In addition, all of other Examples of the present invention andComparative Examples were produced so as to obtain the compositionratios of samples by using the sample that had the impurity C contentand the impurity Si content of the sample No. 3 in Table 1 as the rawmaterials. In addition, multiple samples having varied porosities wereproduced as shown in Tables 2 and 3. On these samples, the sinteringtemperature; the radial crushing strength; the dimensional change; andthe yield, were measured. Then, the corrosion test and the sliding testwere performed on these samples.

Dimensional Change (DC):

The outer diameter of the green compact was measured before sintering inadvance; and sintering was performed. Then, the dimension of thesintered material (the sintered sliding material) after sintering wasmeasured; and the dimensional change before and after sintering wasobtained by calculation.

Yield:

The yield was obtained as the ratio in which the dimension after sizingwas within the tolerance range. Grading was based on the measurementresults of 50 samples. In the case where 96% or more satisfied thecriteria, it was graded “A.” In the case where 90% or more and less than96% satisfied the criteria, it was graded “B.” In the case where lessthan 90% satisfied the criteria, it was graded “C.”

Corrosion Test:

The organic acid test solution, which emulated inferior quality gasoline(pseudo inferior gasoline), was prepared by adding carboxylic acidrepresented by the formula, RCOOH (R was a hydrogen atom or ahydrocarbon group), to gasoline.

The pseudo inferior gasoline was prepared by adding the organic acid inabout 5-times higher concentration than the conventional pseudo inferiorgasoline corresponding to the decomposed biofuel.

The multiple bearing parts 1 for testing were immersed in this organicacid test solution in a warm bath (60° C.) for 500 hours.

After the corrosion test, products adhered to the surface of the bearingpart 1 were removed by chemical. Then, the mass change rate between: themass before immersing in the organic acid test solution: and the mass ofthe bearing part 1 after removal of the adhered products after immersionwas measured. In the corrosion resistance columns of each Table, thegrade “A” or “B” is shown. The grade “A” indicates that the mass changerate satisfied, 0%≥(the mass change rate)≥−0.40% in the sample. Thegrade “B” indicates that the mass change rate satisfied, −0.40%>(themass change rate) in the sample.

Sliding Test:

The wear resistance test was performed in the condition where thebearing was subjected to high pressure and fast flowing gasoline by:circulation of gasoline in a narrow space at high speed; and high speedrotation of the motor causing the fast flowing gasoline.

The bearing part was installed on a fuel pump having the outer lengthdimensions of 110 mm×40 mm; and this fuel pump was placed in thegasoline tank. Actual machine test was performed in the condition of:5,000-15,000 rpm of the impeller rotation speed; 50-250 L/hour of theflow of gasoline; 500 kPa at maximum of the pressure loaded on thebearing due to high speed rotation; and 500 hours of the test time. Thegrade “A” indicates that the maximum wear depth on the bearing surfaceafter the test satisfied, 0 μm≤(the maximum wear depth)≤10 μm in thesample. The grade “B” indicates that the maximum wear depth on thebearing surface after the test satisfied, 10<(the maximum wear depth) inthe sample.

TABLE 1 C content and Si C content and Si content as impurities contentas impurities in raw material powder in sintered material SinteringDimen- Sliding Component composition (mass %) (mass %) temper- sionalYield charac- Corrosion Sintered sliding (mass %) Impurity ImpurityImpurity Impurity ature Change A, B, teristics resistance material Ni SnP C Cu C Si C Si (° C.) (%) or C A or B A or B Example of 1 55 9 0.2 5balance 0.005 0.015 0.008 0.017 1050 +0.13 A A A the present 2 55 9 0.25 balance 0.013 0.020 0.031 0.016 1030 +0.37 A A A invention 3 55 9 0.25 balance 0.035 0.030 0.027 0.024 1050 +0.64 A A A 4 55 9 0.2 5 balance0.210 0.041 0.190 0.042 1080 +0.79 B A A 5 55 9 0.2 5 balance 0.43 0.0700.37 0.075 1050 +0.81 B A A 6 55 9 0.2 5 balance 0.61 0.150 0.60 0.151050 +1.15 B A A Comparative 7 55 9 0.2 5 balance 0.91 0.183 0.87 0.181080 +2.83 C A A Example 8 55 9 0.2 5 balance 1.14 0.130 1.05 0.14 1050+3.14 C A A

TABLE 2 Radial Component composition Sintering crushing DimensionalYield Sliding Corrosion Sintered sliding (mass %) temperature Porositystrength change A, B, characteristics resistance material Ni Sn P C Cu(° C.) (%) (N/mm²) (%) or C A or B A or B Example of 3 55 9 0.2 5balance 1050 13.8 320 +0.64 A A A the present 9 55 9 0.2 5 balance 10208.1 435 +0.97 B A A invention 10 55 9 0.2 5 balance 1050 18.7 284 +0.49A A A 11 55 9 0.2 5 balance 1050 25.2 236 +0.30 B A A 12 55 9 0.2 5balance 1050 28.0 203 +0.23 B A A 15 36 9 0.2 5 balance 960 15.0 238+0.97 B A A 16 40 9 0.2 5 balance 980 15.9 272 +0.84 A A A 17 75 9 0.2 5balance 1090 15.0 416 +0.51 B A A 18 86 9 0.2 4 balance 1120 15.1 515+0.32 B A A 19 55 1 0.2 5 balance 1050 14.9 298 +0.25 A A A 20 55 3 0.25 balance 1030 14.8 335 +0.17 A A A 21 55 6 0.2 5 balance 1050 16.1 363+1.08 A A A 22 55 11 0.2 5 balance 1050 14.6 330 +1.41 B A A 23 55 90.05 5 balance 1050 15.4 286 +1.23 B A A 24 55 9 0.4 5 balance 1050 15.4363 +0.68 B A A 25 55 9 0.75 5 balance 1010 14.7 384 +0.75 B A A 26 55 91 5 balance 1070 15.5 471 +0.78 B A A 27 55 9 0.2 1 balance 1050 15.4620 −0.22 B A A 28 55 9 0.2 2 balance 1050 15.9 500 +0.16 A A A 29 55 90.2 3 balance 1050 15.2 443 +0.17 B A A 30 55 9 0.2 7 balance 1080 14.6303 +0.98 B A A 31 55 9 0.2 9 balance 1050 14.4 271 +1.34 B A A

TABLE 3 Radial Component composition Sintering crushing DimensionalYield Sliding Corrosion Sintered sliding (mass %) temperature Porositystrength change A, B, characteristics resistance material Ni Sn P C Cu(° C.) (%) (N/mm²) (%) or C A or B A or B Comparative 13 89 9 0.2 1balance 1160 7.1 713 +2.01 C B A Example 14 55 9 0.2 11 balance 105029.6 168 +0.11 B B B 32 25 9 0.3 5 balance 900 15.3 230 +1.02 A A B 3330 9 0.2 5 balance 925 14.6 232 +1.31 B A B 34 55 0 0.2 5 balance 105015.2 274 +0.48 A A B 35 55 0.5 0.2 5 balance 1050 14.5 286 +0.31 A A B36 55 12 0.2 5 balance 1020 14.7 324 +2.24 C A A 37 55 15 0.2 5 balance1050 15.5 310 +2.39 C A A 38 55 9 0 5 balance 1050 14.5 268 +1.80 C A B39 55 9 1.25 5 balance 1030 14.9 514 +1.65 C A A 40 55 9 0.2 0 balance1050 14.9 709 −0.63 A B A 41 55 9 0.2 0.5 balance 1080 15.0 660 −0.30 AB A

The samples Nos. 1-6 in Table 1 were the samples in which both contentsof C and Si as impurities were reduced. In each of these samples, thedimensional change was low, and the yield was excellent.

The sample No. 7 was the sample in which both contents of C and Si asimpurities were high; and the dimensional change was high. The sampleNo. 8 was the sample in which only the C content as impurities was high,the C content exceeding 1%. In this sample No. 8, the dimensional changebecame even higher. In any one of samples Nos. 7-8, the yield was bad.

Each of the samples Nos. 13, 14, 32-41 in Table 3 had the C and Sicontents as impurities of the sample 3 in Table 1, and the contents ofNi, Sn, P, and C were defined as shown in Tables 2 and 3 as othercompositions.

The samples 9-12 in Table 2 were the samples, in which the contents ofNi, Sn, P, and C were identical, but the sintering temperature waschanged to 1020° C. or 1050° C.; or the porosity was changed within therange of 8.1-28%. In each of the samples 9-12, the dimensional changewas low; and the yield was excellent. In addition, both of the slidingcharacteristics and the corrosion resistance were excellent. The valueof the porosity and the radial crushing strength were in reverseproportional relationship. When the porosity was less than the range of8-28%, the radial crushing strength tended to be too high. When theporosity was higher than the range of 8-28%, the radial crushingstrength tended to be too low.

The samples Nos. 15-18 in Table 2 were the samples which were producedby varying their Ni contents. In each of the samples Nos. 15-18, theyield, the sliding characteristics, and the corrosion resistance wereexcellent. Contrary to that, there was a problem in corrosion resistancein the samples Nos. 32-33 shown in Table 3, in which the Ni contentswere low. In addition, both of the yield and the sliding characteristicswere deteriorated; and the dimensional change was high in the sample No.13, in which the Ni content was too high.

The samples Nos. 19-22 in Table 2 were the samples which were producedby varying their Sn contents. In each of the samples Nos. 19-22, theyield, the sliding characteristics, and the corrosion resistance wereexcellent. Contrary to that, there was a problem in corrosion resistancein each of the sample No. 34 free of Sn in Table 3 and the sample No. 35having a low Sn content. In the sample No. 36 having the too high Sncontent, the yield was deteriorated; and the dimensional change washigh. In the sample No. 37 having even higher Sn content than the sampleNo. 36, the yield was deteriorated; and the dimensional change becameeven higher

The samples Nos. 23-26 in Table 2 were the samples which were producedby varying their P contents. In each of the samples Nos. 23-26, theyield, the sliding characteristics, and the corrosion resistance wereexcellent. Contrary to that, there was a problem in the yield and thecorrosion resistance in the sample No. 38 free of P. In addition, theyield was deteriorated in the sample No 0.39 having a too high Pcontent.

The samples No. 27-31 in Table 2 were the samples which were produced byvarying their C contents. In each of the samples Nos. 23-26, the yield,the sliding characteristics, and the corrosion resistance wereexcellent. Contrary to that, there was a problem in the slicingcharacteristics in the sample No. 40 free of C. In addition, in thesample No. 41 having a low C content, the sliding characteristics weredeteriorated. Comparative Example 14 in Table 3 is an example having atoo high C content. In Comparative Example 14, the radial crushingstrength was low; and the sliding characteristics and the corrosionresistance were deteriorated.

Based on the results described above, it was demonstrated that thesintered sliding material, in which the dimensional change was low; theyield was excellent; the sliding characteristics were excellent; and themass change was low in the corrosion resistance test, could be provided,if the sintered sliding material had the composition satisfying therelationship of: 36-86% of Ni; 1-11% of Sn; 0.05-1.0% of P; 1-9% of C;and the Cu balance, while the C content and the Si content as impuritieswere kept at low amounts.

FIG. 4 is a drawing showing the state of the surfaces of theconventional example (the sample No. 32 in Table 2) and Example of thepresent invention (the sample No. 3) before the test and after immersionin the organic acid-containing gasoline. An enlarged part of the surfaceis shown in the drawing.

Compared to the conventional example (No. 32), it was demonstrated thata better surface condition was obtained even after immersion in theorganic acid-containing gasoline in the sample of Example of the presentinvention (No. 3).

INDUSTRIAL APPLICABILITY

A Cu-based sintered bearing having excellent corrosion resistance, heatresistance, wear resistance; and high dimensional accuracy can beprovided.

REFERENCE SIGNS LIST

-   -   1: Bearing part    -   2: Fuel pump    -   3: Casing    -   5: Motor (armature)    -   6: Rotating shaft    -   7: Impeller    -   8: Inlet    -   9: Outlet    -   11: Alloy grain    -   12: Pore    -   13: Free graphite    -   15: Sintered sliding material

1-13. (canceled)
 14. A method of producing a sintered sliding materialwith excellent corrosion resistance, heat resistance, and wearresistance, the method comprising the steps of: obtaining a mixed powderby mixing a plurality of powders containing one or more among Cu, Ni,Sn, P, and C in such a way that a total composition of the mixed powderbecomes: 36-86 mass % of Ni; 1-11 mass % of Sn; 0.05-1.0 mass % of P;1-9 mass % of C; and the Cu balance by using at least one of: a Cu—Nialloy powder in which a C content is 0.6 mass % or less and a Si contentis 0.15 mass % or less as inevitable impurities; and a Ni—Cu alloypowder in which a C content is 0.6 mass % or less and a Si content is0.15 mass % or less as inevitable impurities; producing a green compactby pressing the mixed powder; and obtaining a sintered sliding materialhaving a structure containing: an integrated matrix; and free graphitedispersed in a plurality of pores by sintering the green compact at960-1140° C. so that a plurality of grains of alloy made of a Cu—Nialloy or a Ni—Cu alloy disperse in the plurality of pores in the grainboundaries of the plurality of grains of alloy.
 15. The method ofproducing a sintered sliding material with excellent corrosionresistance, heat resistance, and wear resistance according to claim 14,wherein the mixed powder is obtained by mixing: at least one of a Cu—Nialloy powder and a Ni—Cu alloy powder; a Sn powder; a Cu—P alloy powder;and C powder.
 16. The method of producing a sintered sliding materialwith excellent corrosion resistance, heat resistance, and wearresistance according to claim 14, wherein a porosity of the sinteredmaterial is 8-28%.
 17. The method of producing a sintered slidingmaterial with excellent corrosion resistance, heat resistance, and wearresistance according to claim 14, wherein as inevitable impurities inthe matrix, a C content is 0.002 mass % to 0.6 mass %, and a Si contentis 0.015 mass % to 0.15 mass %.